1. Field
Apparatuses and methods consistent with exemplary embodiments relate to a Voice over Internet Protocol (VoIP) gateway device, a control method thereof, and a VoIP gateway system, and more particularly, to a VoIP gateway device, a control method thereof and a VoIP gateway system which provides a call back service.
2. Description of the Related Art
Voice over Internet Protocol (VoIP) relates to a set of communication service technologies which performs fax transmission/reception or voice calls such as telephone calls in a general telephone network (e.g., a Public Switched Telephone Network (PSTN)) by converting voice or fax data into a data packet of the Internet Protocol in a computer network. FIG. 1 illustrates a related art VoIP system. As shown therein, a sender terminal and a receiver terminal are VoIP terminals, and a proxy server relays VoIP communications between the sender terminal and the receiver terminal. If the sender terminal transmits an invite message to the proxy server to request a call connection to the receiver terminal, the proxy server transmits the invite message to the receiver terminal (201). If the receiver terminal is busy and unavailable to receive the call, the proxy server reports the same to the sender terminal (201). In this case, the sender terminal may register a call back service with the proxy server (202). Once the call back service is registered, the proxy server identifies the state of the receiver terminal and reports an available time to the sender terminal (203). In response to such a report, the sender terminal again transmits the invite message to the receiver terminal through the proxy server (204).
In the related art, to use the call back service which is provided for the case where a call connection requested by the sender is not available due to the receiver's circumstances, the proxy server should perform the call back function, or software of the proxy server should be changed. VoIP is based on session initiation protocol (SIP), according to which only a call service for a failure to connect an outgoing call is defined, but a call service for a failure to receive an incoming call is not defined. If the state of the receiver terminal is not identifiable at the time when the proxy server performs the call back function, notify ring timeout occurs and no report is made to the sender terminal.